Sens. Patrick Leahy (D-Vt.) and Bernie Sanders (I-Vt.) on Friday lambasted their Republican colleagues for breaking precedent by refusing to allow the U.S. Senate to consider witnesses in the impeachment trial of President Donald Trump.

Vermont's two U.S. Senators voted in favor of a motion that would allow witnesses to testify. But the effort fell short, 51-49, despite two Republicans crossing the aisle to vote in favor — all but confirming the country’s third-ever impeachment trial will soon reach its finale.

Minutes after the vote, Leahy told Seven Days the decision means that, for the first time in American history, an impeachment trial may conclude without any witness testimony.

"It just boggles the mind," he said in a phone interview.

The former prosecutor further condemned the process in a statement before Friday's vote, saying it reminded him of the trial depicted in Alice in Wonderland, during which a jury is asked to consider its verdict moments after hearing the accusations.

"But even in that case it was acknowledged that 'There’s a great deal to come before that,' and the first witness was called," Leahy wrote. "With apologies to Lewis Carroll, surely the United States Senate can at least match the rigorous criminal procedure of Wonderland?"

Sanders echoed his seatmate's criticism, calling the proceeding a "show trial."

"This is outrageous," he said in a pre-taped video posted to Twitter after the vote. "This is a mockery of justice. And is sadly consistent with a president who believes he is above the law."

"It is a sad day for our country," he added. "It is a sad day for justice. And it is a sad day for democracy. "

Democrats had sought witnesses who could further speak to the central question of the impeachment proceedings: whether Trump withheld Ukrainian aid in exchange for investigations into his political rival.

Calls for further testimony intensified earlier this week when the New York Times reported that Trump's former national security adviser John Bolton alleges in an upcoming book that the president directly linked the aid with the investigations during an August conversation.

But it had become increasingly clear in the days leading up to Friday’s vote that Democrats would not be able to find the necessary support from Republicans, who have offered various rationales for blocking the motion. Some went as far as to say that while the trial had indeed proved that the president committed the acts he's accused of, it's not enough to remove him from office. 

Leahy took to Twitter before the vote to describe it as one of the most “consequential” days of his 45 years in the Senate. He warned his colleagues that their decisions would “define our system of government for years to come.”

“The sum of our public life may be remembered by today,” he wrote.

After the vote, he suggested some of his colleagues across the aisle would be remembered for failing to vote their conscience.

"Even the people who tell you privately they're concerned with what the president did, they’re afraid to cross him and have to face Republican voters at home," he told Seven Days. "Nobody owns a seat in the U.S. Senate."